In conventional applications, all the large scale capacitive touch panels use a surface capacitance sensing technique to scan thereto for determining a touch information, which uses a set of detecting currents, each directed to an endpoint of the large scale touch panel to produce detected values, and therefore, even multiple fingers simultaneously touch the large scale touch panel, this sensing technique still retrieves only one set of detected currents in response to this multi-finger touch. For this reason, the surface capacitance sensing technique can identify only one set of absolute coordinates. In a two dimensional matrix for instance, only one set of parameters (X,Y) will be determined, and thereby it can't implement a multi-finger touch detection.
An all points addressable (APA) projected capacitance sensing technique is capable of implementing a multi-finger touch detection, but not applicable to large scale touch panels because, to implement this sensing technique, it is necessary to charge and discharge each point sensor on the large scale touch panel. Taking a matrix-type touch panel for example, when the X and Y traces increase, the pixel number of an APA projected capacitance touch panel dramatically increases and thereby significantly degrades the frame rate of the touch panel due to the very long time period for scanning the large scale touch panel in a frame.
An axis intersect (AI) projected capacitance sensing technique is also capable of implementing a multi-finger touch detection, but not applicable to large scale touch panels, too. FIG. 1 is a schematic diagram of a conventional AI projected capacitance sensing technique applied to a small scale touch panel 10, in which an AI projected capacitance touch IC 12 is used to scan the small scale touch panel 10. Assuming that the AI projected capacitance touch IC 12 can support up to 22 traces, a good frame rate can be attained for a small scale touch panel 10 having ten X traces TRX1-TRX10 and ten Y traces TRY1-TRY10. However, if a this type touch IC 12 is applied to a large scale touch panel 14 having forty X traces TRX1-TRX40 and forty Y traces TRY1-TRY40, as shown in FIG. 2, the total number of traces that the touch IC 12 needs to scan dramatically increases. Unfortunately, the frame rate of the overall touch panel application is dependent to a very large extent on the time it takes the touch IC 12 to charge and discharge capacitors each time. In other words, the frame rate is determined mainly by the time in a frame that the touch IC 12 charges and discharges the capacitors. Hence, if an AI projected capacitance touch IC capable of scanning a greater number of traces is applied to a large scale touch panel 14, a major drawback would be a significantly decreased frame rate in the overall application, which leads to compromised performance at the application end.
Therefore, it is desired a sensing method applicable to large scale touch panels, capable of implementing a multi-finger touch detection thereto, and maintaining a good frame rate thereof.